Pre-scalping of ferromagnetic contaminants from the fluid to be filtered using magnetic force is prior art for filter devices. Plant machinery that employs a fluid circuit for lubrication and/or cooling of mechanical equipment, such as transmissions or pumps, always have metal particles present in the fluid through friction during operation, in particular in the instance of transmissions that are under high load in heavy machinery such as wind turbines or cement mills. Ferromagnetic contamination of the fluid also occurs in other kinds of process fluids to a varying degree. In particular in detergent solutions often used in plants for the automatic manufacture of parts, a high concentration of ferromagnetic particles can be found in the fluid. The separation of particles significantly increases the service life of the filter elements, particularly in fluids with high contaminant concentrations.
DE 10 2006 062 807 B4 and DE 10 2013 014 453 A1 disclose examples of known devices. As a device that generates a magnetic field, these known filter devices use a magnetic rod with permanent magnets, also called a magnetic core. The magnetic core extends in those devices into the inner space of the respective filter element and is attached to a housing lid of the filter device. The outside of the magnetic rod forms the adhering surface on which the metallic particles are deposited in operation. In order to dispose of the deposits in the known device, the housing lid has to be unscrewed to be able to remove the magnetic rod together with the filter element from the housing. The magnetic rod must then be removed from the filter element to be able to remove the particles that adhere to the outside of the magnetic rod. The removal of these particles is rather difficult since they are retained by the magnetic force on the outside of the magnetic rod. The use of the known filter devices then requires a correspondingly large effort in terms of maintenance and time.
U.S. Pat. No. 8,636,907 B1 discloses a filter device of this kind for fluids, comprising a housing for at least one filter element. The housing has an inlet for supplying the fluid to be cleaned into an unfiltrate chamber of the housing. The unfiltrate chamber is separated by the filter medium of the filter element from a filtrate space of the housing. The filter space is provided with an outlet for filtrate. A magnetic field-generating device is disposed inside the unfiltrate chamber and provides an adhering surface for ferromagnetic particles that adhere thereto due to the magnetic force. At least one casing envelopes the associated magnetic field-generating device. The casing extends from at least one opening in the housing wall into the unfiltrate chamber and in which the respective magnetic field-generating device may be movably accommodated in such a way that it can be inserted into the casing and at least partially removed from it.
In the known solution, the respective casing of the magnetic field-generating device protrudes into the respective filter element itself or between the elements. On the one hand, it impairs the filtration of the unfiltrate supplied via the inlet. On the other hand, it makes it more difficult to remove the respective filter element and replace it with a new one.